v0.4.2

What's Changed

A bunch more improvements to the implementations of diffdrr.renderers.Siddon and diffdrr.renderers.Trilinear. Siddon's rendering time is down to 37.9 ms -> 29.5 ms -> 26.9 ms!

• Make no_grad in Siddon switchable by @eigenvivek in #275
• Add registration example with L-BFGS by @eigenvivek in #277
• Reimplement alphaminimax filtering by @eigenvivek in #279
• Implement alpha filtering in Trilinear by @eigenvivek in #281

Full Changelog: v0.4.1...v0.4.2